Gene therapy is a method of treating diseases by conveying a therapeutic gene into a target organ in the body and by inducing intracellular expressions of new proteins, and is aimed at treating and eliminating not just the symptoms but the cause of disease. Gene therapy has an excellent selectivity, compared with other treatment methods using general drugs, and can be applied for a long period of time because it improves the treatment rate and time of diseases that are hard to treat. Because using DNA as the therapeutic gene is prone to enzymatic hydrolysis in the body and its transfection efficiency is low, it is essential to develop a gene carrier that safely delivers the therapeutic gene into the target cells to achieve a high expression efficiency for effective gene therapy.
A gene carrier must be slightly toxic or non-toxic, and have an ability to deliver the gene into the target cells with selectivity and efficacy. Such gene carriers can be largely divided into viral and non-viral vectors. Up to now, a viral vector having a high transfection efficiency has been used as the gene carrier in clinical trials. However, there are many limitations in the application of viral vectors such as retrovirus, adenovirus, and adeno-associated virus in the human body, because of their complex preparation, safety problems including immunogenicity, risk of infection, inflammation induction, and non-specific DNA insertion, and the limited size of loading DNA. Thus, much attention has been paid to non-viral vectors as an alternative to the viral vectors.
The non-viral vectors have the many advantages of being administered repeatedly with minimal immune response, targeting specific cells, being stable in storage, and being easily produced in large quantities. Examples of the non-viral vectors include cationic liposome-based N-[1-(2,3-dioleyloxy)propyl]-N,N,N-trimethylammonium chloride (DOTMA), alkylammonium, cationic cholesterol derivatives, gramicidin or the like.
Of the non-viral vectors, cationic polymers have recently attracted much attention, because they can form a complex with negatively charged DNA via an ionic bond. These cationic polymers includes poly-L-lysine (PLL), poly(4-hydroxy-L-proline ester), polyethyleneimine (PEI), poly[α-(4-aminobutyl)-L-glycolic acid], polyamidoamine dendrimer, poly[N,N′-(dimethylamino)ethyl]methacrylate (PDMAEMA) or the like. They condense DNA into nanoparticles to protect DNA from enzymatic degradation, and facilitate its cellular uptake to enhance endosomal escape. Compared to viral vectors, most non-viral vectors have the advantages of biodegradability, low toxicity, non-immunogenicity, ease of use or the like, but there are still present the problems of relatively low transfection efficiency, limited particle size or the like.
In particular, most of the cationic polymers used as non-viral vectors exhibit a high transfection efficiency in vitro under a low-serum environment, but the cationic polymer/gene complex shows a remarkably low transfection efficiency due to a variety of factors present in the serum under in vivo environments, resulting in a poor intracellular influx of the gene. This is attributed to the non-specific interaction of excessive positive charges on the surface of the cationic polymer/gene complex with the plasma proteins and blood components in vivo. That is, the transfection efficiency of the cationic polymer is remarkably reduced in the presence of a large amount of serum in vivo, not under serum-free or very low serum conditions in vitro. When applied as it is in the body, the cationic polymer can be agglomerated and accumulated in the lung, liver and spleen, and also removed by opsonization via the reticuloendothelial system. Therefore, therapeutic applications of the cationic polymers are very limited. Polyethyleneimine (PEI), one of the most widely investigated non-viral vectors, also has the drawbacks of very low transfection efficiency in vivo, high cytotoxicity, and low gene expression efficiency due to low blood compatibility.
Therefore, there is an urgent need to develop a gene carrier having an enhanced transfection efficiency while maintaining the advantages of the conventional non-viral vectors.
Accordingly, the present inventors have endeavored to develop a gene carrier having low cytotoxicity and high transfection efficiency. As a result, they found that a polysorbitol-based osmotically active transporter (PSOAT) prepared by Michael addition between polyethyleneimine (PEI) and a sorbitol-based derivative shows very low cytotoxicity in vitro and in vivo, and has an osmotic activity due to a sorbitol skeleton and a proton sponge effect due to a polyethyleneimine (PEI) skeleton so as to exhibit a remarkably improved transfection efficiency, and thus the polysorbitol-based osmotically active transporter can be used as a gene carrier for gene therapy, thereby completing the present invention.